1. Field of the Invention.
The present invention relates to linear distance measuring devices that have compact mounting heads and which provide enhanced output signals.
2. Description of the Prior Art
U.S. Pat. No. 3,898,555 issued to the present inventor shows a linear distance measuring device of the type described herein, which uses a sonic waveguide, and The waveguide is tubular with a wire running through the center. A current pulse is sent through the wire, and a magnet that is positioned adjacent to the waveguide causes a torsional strain wave when the current pulse interacts with the magnetic field from the magnet. The torsional pulse in the waveguide is transmitted as a torsional strain wave that has a time period and which is reflected back to the waveguide mounting structure. The twisting or torsional movement is sensed by a mode converter, which provides an output signal, the output signal of the return strain wave is correlated compared to the time of launch of the current pulse causing the torsional strain wave for determining the distance to the magnet from the converter The time interval between the application of the electrical pulse and the reception of the torsional pulse by the converter indicates the position of the magnet.
U.S. Pat. No. 4,721,902 shows a noise rejection circuitry for use in the type of transducer shown in U.S. Pat. No. 3,898,555 to insure identifying the return pulse and correlating it properly to a current pulse. Patent No. '902 points out the problems of attempting to raise the return signal level from the mode converter in order to improve the signal-to-external interference noise ratio and indicates that the amplitude of the mode converter signal based on the torsional strain wave is difficult to raise higher than the noise amplitude.
The present invention provides a simple, long sought after solution to the problem of raising the amplitude of the signal received by the mode converter. The problems of low level signals are further compounded by the long length of waveguides that are now being used. Waveguide lengths of 25 feet are commonly used and lengths of 60-80 feet are in use.